A working machine includes, for example, a workshop for machining workpieces using tools such as drills and milling cutters, and a control room for controlling processing machinery in the workshop. Control devices such as a driver and a computer are housed in the control room. The processing machinery and the control devices are connected by cables. A wiring opening is opened in a housing of the control room to allow the passage of the cables. A cable holding tool that functions to hold the cables and also functions to block outside air is attached to the housing of the control room. The working machine is arranged inside a factory. Air inside the factory contains dust, oil, coolant fluids, or the like. When the air containing these matters enters the control room, they cause malfunctioning of the control devices. Therefore, the cable holding tool prevents the penetration of the air containing the above matters into the control room through the wiring opening.
A conventional cable holding tool shown in FIG. 10 and FIG. 11 is known (see patent document 1: Japanese Unexamined Utility Model Application Publication No. S61-179784). FIG. 10 is a plan view of the conventional cable holding tool, and FIG. 11 is a perspective view thereof. In FIG. 10, reference numeral 1 represents a housing of the conventional cable holding tool, reference numeral 2 represents a cable passing through the housing 1, reference numerals 3a and 3b represent soft members such as sponges, and reference numerals 4a and 4b represent pressing tools for pressing the soft members 3a and 3b. As shown in FIG. 11, the cable 2 can be held and the wiring opening of the housing 1 can be sealed by sandwiching the cable 2 between the elastically deformable soft members 3a, 3b. 
However, with the conventional cable holding tool, small gap(s) 5 (see FIG. 10) are formed at a position where the soft members 3a, 3b are coming together to sandwich the cable 2. As a result of this formation a problem may arise in that inside of the housing 1 communicates with outside air via the gap(s) 5. To solve this problem, it has been proposed to provide a plurality of slits on surfaces of the soft members 3a, 3b that contact the cable 2 to thereby improve elasticity of the soft members 3a, 3b such that the formation of the gap(s) is prevented, but this solution made no changes in the formation of the small gap(s).
Therefore, an object of the present invention is to provide a cable holding tool capable of reducing a size of the gap(s) formed at a position where soft members are sandwiching the cable to thereby increase air-tightness thereat.